The present invention relates to a wiring structure in like a liquid crystal display (LCD), and more particularly to a structure, apparatus and method for supplying an averaged voltage to a plurality of LSIs that are connected in a chain-like manner (i.e., one after another).
In recent years, a liquid crystal panel (LCD panel) on which an image is displayed is required to be low in cost. As one means to keep the cost down, Chip On Glass (COG) is commonly known. COG is the technique to mount a couple of or dozens of LCD driver LSI chips, which are provided for one LCD panel, intact on a glass substrate. Also suggested is the combination of COG being combined with Wiring On Array (WOA) that implements the wiring on the glass. According to the COGandWOA technique, it becomes possible to attach the LSI itself directly to the glass substrate, and at the same time, omit the wiring that is presently put on the printed circuit board, so that the cost of production can be vastly lowered and can be granted the requests for a narrow frame in recent years.
On the other hand, there have been some proposals as to the method for achieving the wiring of LCD driver LSIs on glass substrates. For example, one of them is to reduce the number of input signals of LCD driver LSIs to reduce a necessary wiring area, in order to achieve the wiring in frame portions of glass substrates. In addition, the present applicant previously proposed a technique that achieves a fast serial video transfer peculiar to LCD driver LSIs by means of cascade connections (Japanese Patent Application No. Hei 11-351784). Furthermore, there has been proposed a technique to reduce the number of wiring for reference voltage, which must be provided on glass substrates, by generating a reference voltage for y compensation in LCD driver LSIs.
By using the WOA technique, external PCB or Flexible Printed Circuit (FPC) that have been used for the wiring of LCD driver LSIs are no longer needed, whereby drastic cost reduction can be achieved. Also, since mechanical connections are reduced drastically, good results are expected about yield rate.
However, in conventional liquid crystal panels, generally a wiring on glass substrates consists of a very thin metal (2500 xc3x85) and results in high resistance wiring whose sheet resistance is about
0.16xcexa9/xcexcm. With this high resistance wiring, it is impossible to supply uniform voltage to a plurality of LCD driver LSIs, whereby tens to hundreds mV of voltage difference occurs on the voltages which individual LCD driver LSIs receive, due to the voltage drop in the wiring paths. In case of supplying the reference voltage for y compensation, this voltage difference appears as a gradation difference of every LCD driver LSI, whereby uniformity of outputs can not be maintained due to this gradation difference, which results in significant deterioration in image quality. In light of that, in conventional liquid crystal panels, the wiring to supply the reference voltage for xcex3 compensation can not be provided on the glass substrate, so there has been little choice but to configure in a manner where the wiring with sufficiently low resistance is provided on the external PCB (Printed Circuit Board) or FPC, in order to supply the reference voltage to each LCD driver LSI
On the other hand, a method for supplying the uniform voltage is conceivable by making the thickness of metal wiring sufficiently thick or making wiring widths sufficiently wide on the glass substrate, in order to ensure low resistance. However, making the thickness sufficiently thick can cause an increase of process occupied time or other adverse effects on the yield rate of TFT arrays for the production of LCD panels. In case of making wiring widths sufficiently wide, it is necessary to make frame portions of TFT arrays larger in order to secure a wiring space, which greatly runs counter to the requests in recent years. Namely, thought it is possible to provide wiring with low resistance with changing thickness or materials of wiring, which can not sufficiently lead to cost savings and a narrow frame, resulting in no use in employing WOA technique.
Furthermore, in order to generate a reference voltage for xcex3 compensation, a technique is commonly used where an input voltage is divided by ladder resistors provided in the LCD driver LSIs to generate an intended voltage. In this technique, when the wiring of the reference voltage for xcex3 compensation is done by low resistance wiring, a practically unquestionable performance can be achieved, however, with the conventional wiring on the glass, which has high resistance, it is impossible to deliver its thorough performance.
In light of these above technical problems, it is an object of the present invention to reduce the difference of voltages that each LSI receives, in the individual LSIs connected in a chain-like manner (i.e., one after another).
The present invention is directed to an apparatus for supplying a voltage for xcex3 compensation to a plurality of driver LSIs mounted on the same substrate as the one on which liquid crystal cells are formed, by using a wiring structure of high resistivity formed on the same substrate. Namely, an LCD module according to the present invention consists of liquid crystal cells forming an image display area on a substrate; a plurality of driver LSIs mounted on this substrate for applying voltages to the liquid crystal cells; and a wiring structure formed on this substrate for supplying a voltage to the plurality of driver LSIs, wherein this wiring structure supplies the voltage to the plurality of driver LSIs, with the wiring whose resistance gradually changing from a voltage supply point. Also, it is characterized in that this wiring structure supplies the voltage to the plurality of driver LSIs via a forward wiring and a backward wiring. Furthermore, it is characterized in that the forward wiring and the backward wiring are connected like a single stroke of the brush to supply the voltage to the plurality of driver LSIs. Note, considering the present invention as a computer, such as a notebook-sized personal computer, the present invention further includes a host for executing an application, and a plurality of driver LSIs mounted on the substrate for applying voltages to the liquid crystal cells based on a signal from the host.
In another aspect of the present invention, a liquid crystal display according to the invention consists of liquid crystal cells forming a image display area on a substrate; a plurality of driver LSIs mounted on this substrate for applying voltages to the liquid crystal cells; and a wiring structure formed on this substrate for supplying a voltage supplied from a voltage supply point to the plurality of driver LSIs; wherein this wiring structure consists of a forward wiring that starts wiring of the driver LSIs from a driver LSI located near the voltage supply point up to a downstream driver LSI in order, thereby supplying the voltage to the driver LSIs; and a backward wiring that starts wiring of the driver LSIs from the downstream driver LSI up to the driver LSI located near the voltage supply point in order, thereby supplying the voltage to the driver LSIs; wherein the directions of voltage drop in the forward wiring and the backward wiring are opposite.
The wiring structure is characterized in that, in the forward wiring, a wiring width is gradually reduced from the wiring for the driver LSI located near the voltage supply point to the wiring for the downstream driver LSI, whereas in the backward wiring, a wiring width is gradually reduced from the wiring for the downstream driver LSI to the wiring for the driver LSI located near the voltage supply point, thereby enabling to gradually change the wiring resistance by means of wiring widths, so that the slope of voltage drop is controlled with a simple wiring structure on the substrate.
It is also characterized in that, the plurality of driver LSIs includes input pads and output pads for connection corresponding respectively to the forward wiring and backward wiring of the wiring structure, wherein the input pads and the output pads are connected by the wiring inside the plurality of driver LSIs, whereby the plurality of driver LSIs are connected in cascade connection by this wiring structure, wherein WOA is implemented with increasing the efficiency of the wiring of the substrate. In addition, it is characterized in that the plurality of driver LSIs are bus-connected to the forward wiring and the backward wiring of this wiring structure, whereby a reference voltage for xcex3 compensation is supplied not through the metal wiring inside the driver LSIs.
In a further aspect of the invention, the present invention is directed to a wiring structure which supplies a voltage to a plurality of LSIs arranged at a specified interval apart, comprising: a voltage supply point receiving a voltage; and a wiring section that starts wiring of the LSIs from a LSI located near the voltage supply point up to a downstream LSI in order, thereby supplying the voltage to the plurality of LSIs; wherein the wiring width is gradually reduced toward the downstream side. Furthermore, this wiring section includes a forward wiring that is provided from the voltage supply point toward the downstream LSI; and a backward wiring that is provided from the downstream LSI toward the LSI located near the voltage supply point, wherein the backward wiring supplies the voltage to the plurality of LSIs with the wiring width being gradually reduced from the downstream LSI toward the LSI located near the voltage supply point.
In a further aspect of the invention, the present invention is directed to a wiring structure which supplies a voltage to a plurality of LSIs arranged at a specified interval apart, comprising: a forward wiring and a backward wiring on a substrate on which a plurality of LSIs are arranged, wherein a wiring resistance of the wirings gradually changes; wherein the voltage is supplied to the plurality of LSIs from both the forward wiring and the backward wiring.
Further, it is characterized in that the forward wiring and the backward wiring are detached from each other, and the forward wiring and the backward wiring are supplied a voltage from different voltage supply points, whereby the voltage is supplied to the plurality of LSIs with keeping an offset voltage small.
Moreover, it is characterized in that the forward wiring and the backward wiring are concatenated, and the forward wiring and the backward wiring are supplied a voltage from the same voltage supply point, whereby the voltage supply point is unified at one place, resulting in simplification of the wiring structure.
In a further aspect of the invention, the present invention is directed to a method for supplying a voltage to a plurality of LSIs mounted on a substrate, the method comprising the steps of: wiring the plurality of LSIs on the substrate using a forward wiring and a backward wiring whose wiring resistance gradually changes; the plurality of LSIs receiving a voltage from both the forward wiring and the backward wiring; and the plurality of LSIs time-averaging the received voltage to generate a reference voltage.
More specifically, a wiring resistance used for the forward wiring and the backward wiring gradually changes, wherein the wiring resistance between adjacent LSIs gradually changes with the ratio of approximately 1/(Nxe2x88x921), 1/(Nxe2x88x922), 1/(Nxe2x88x923), . . . , 1/1 in order (where N is the number of connected LSIs). According to this configuration, it is possible to adjust the slope of voltage drop to be almost linear, whereby the slopes of voltage drop in the forward and backward wirings are in an opposite direction each other, so that the time-average of voltage is kept constant among each LSI.
In a further aspect of the invention, the present invention is directed to a method for supplying a voltage to a plurality of driver LSIs mounted on a substrate, the method comprising the steps of: providing a wiring of high resistivity which gradually changes the wiring width on this substrate; connecting the plurality of driver LSIs to the wiring of high resistivity in order; supplying a voltage to the wiring of high resistivity; supplying a voltage to the driver LSIs via the wiring of high resistivity, wherein a voltage drop occurs between the individual driver LSIs; and generating a reference voltage for xcex3 compensation in the driver LSIs based on the supplied voltage, thereby making use of the voltage drop positively to output a nearly uniform value for xcex3 compensation. It is characterized in that, the provided wiring of high resistivity consists of a forward wiring which supplies a voltage to the driver LSIs from a voltage supply point in order which supplies a voltage to this wiring, and a backward wiring which supplies a voltage to the driver LSIs toward the voltage supply point in order, wherein the forward wiring and the backward wiring are connected.
Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views.